In German Printed Application (Auslegeschrift) DT-AS 25 43 501, there is described a tracked vehicle for the excavation of subterranean courses in the production of tunnels and the like which comprises a forwardly extending machine beam having one or more excavating drums which generally are intended to cut the face of the subterranean structure along the bottom of the excavation to be produced therein. In addition, the vehicle carries an outrigger excavator which can cut upper portions of the face. The milling or cutting head on this arm, which is swingable about a vertical axis and can be raised and lowered with respect to a horizontal axis, is rotated, in turn, about an axis of rotation which generally extends in the direction of advance of the vehicle.
While this apparatus has been found to be highly effective with respect to a highly stable subterranean structure, problems are encountered when the structure is not highly stable and timbering is required proximal to the cutting operation. While the vehicle is generally provided with means for timbering or affording roof support immediately downstream of the beam and vehicle structure, this does not always suffice.
There is also known a tunnel-excavating machine, generally referred to as a DEMAG apparatus, which is provided with an outrigger arm having an excavating head without the aforementioned excavating drum for undercutting the face to be excavated. In this apparatus, however, means is provided for supporting the roof of the excavation and such means includes a cantilevered cap which reaches forwardly close to the cutting operation. Such apparatus can be used in less stable structures but it has been found that problems are encountered primarily with respect to the transfer of vibration to the roof-supporting unit. As a consequence, high-frequency oscillations can develop in the machine which can approach the characteristic or resonance vibration frequency thereof and endanger the tunnel-excavating operation as well as the machine itself. Particularly massive support units are required to brace the machine against these vibration phenomena.